Taylor Swift Calls Rocking with Def Leppard 'A Dream'

Taylor Swift's first exposure to Def Leppard's tunes? In the womb. The 18-year-old country princess, who paired with the '80s rock icons to tape an upcoming episode of CMT Crossroads in Nashville Oct. 6, tells PEOPLE that her love affair with the band began before she was born.

"My mom was a huge fan of theirs when she was pregnant with me," Swift says. "So growing up, the music that was playing in my house was Def Leppard. It was music that she liked that I could like too."

Swift set about contacting the band a year ago in hopes that they'd join her onstage for CMT's genre-bending series. The lads from Sheffield, England, whose blockbuster Hysteria album was released two years before Taylor was born, admit they were clueless to her fame at first.

"The first thing we did is Google 'Taylor Swift' and we were like, 'Whoa! She's only a kid!'" said Def Leppard frontman Joe Elliott. "Then you start listening to the songs and it's like, 'Why wouldn't we want to do this?' I mean she's one of the biggest stars in America now. It's flattering."

The collaboration resulted in a few unexpected moments – like Elliott joining Swift in the chorus of her new song, "Love Story," crooning along with the lines, "You'll be the prince and I'll be the princess."

Says Elliot with a laugh, "I'm comfortable with my feminine side!"

At the Crossroads taping (airing Nov. 7), the artists teamed up on Def Leppard classics like "Pour Some Sugar on Me" and Swift's hits such as "Picture to Burn."

"This is my childhood dream come true," Swift told the crowd after singing Def Leppard's "Photograph." "I'm freaking out that that just happened!"